1. Field of the Invention
The invention relates to address routed communication, such as packet switched sessions, carrying continuous types of media and more particularly to continuing or maintaining the communication through address changes.
2. Background Information
In communication systems, there are two general types of communication routing. One type uses what is generally referred to as a circuit switched routing system. The other type uses what is generally referred to a packet switched, or address routed system.
In a circuit switched system, a communication session is established between two or more terminals and the required communication resources (bandwidth, channels, etc.) are assigned to the session until the session ends, or otherwise changes. The public switched telephone network (PSTN) is generally considered a circuit switched system. A call is assigned communication resources when the caller places the call and those resources are indefinitely assigned to that call. In a circuit switched system carrying voice communications, signal latency is typically a primary design consideration, while signal loss or distortion is a secondary design consideration. In simple terms, fast is better than perfect. This is appropriate for voice communication, where a person adjusts to distortion or loss in quality much easier than they adjust to delay.
With the advent of data networks and the need to transport data between and across those networks, a different type of communication system has evolved. These data networks typically establish a communication session using a communication stream that is divided into individually addressed data bursts or packets. These information packets have address information appended to the data and are routed across the communication medium using that address information. However, in contrast to a circuit switched network, the connections for this type of communication are established by a switching matrix that routes the data packets based on the appended address information. As the switching matrix and loading changes dynamically, individual data packets are frequently routed through different paths from the source to the destination, arriving out of order. To compensate for the change in order, some form of data buffering is required at the receiver, which can introduce delay. In addition, error correction may require that data packets be re-transmitted if the receiving terminal detects an error. Buffering and error correction both introduce delay. In a packet switched communication system, a primary consideration is maintaining data integrity and eliminating errors, while a secondary consideration is data latency. In simple terms, information integrity and fidelity is better than speed of delivery for most data. This is of course appropriate for data, where the data may have no value if it includes a single error.
There are a number of known data networking protocols, which include: TCP/IP; UDP/IP; NetBEUI; and IPX/SPX. Most of these data networking protocols are appropriate for packet switched or address routed communication, though they may have been developed for specialized applications or equipment.
Different transport media are integrated and part of the circuit switched and packet switched communication transmission systems. Some transmission systems use wired transport media and others use wireless. Wired or terrestrial transmission systems include twisted pair, coaxial, and fiber optic. Other assorted transmission systems, which are used in conjunction with wireless systems include light frequency, and radio frequency systems. Some of these transport media are more commonly associated with circuit switched systems and other transport media are more commonly associated with packet switched systems. However, the inter-connection and cross-over of the different types of systems is on-going.
In addition, there are hybrid protocols and services, such as Asynchronous Transfer Mode (ATM). From the user perspective, ATM service can provide what appears to be a virtual circuit switched session using packet switched protocols. This is because the user can request and get a quality of service guarantee (the users request or reserve a specified signal latency, with specified error tolerance).
Many of these different protocols and media have been adapted to handle large bandwidth real-time applications from fixed point to fixed point. As a result, a user at a desktop computer can connect using a wired or wireless connection to a streaming multi-media server over the Internet using packet switching techniques and protocols and participate in a streaming multi-media session that displays characteristics of a circuit switched network.
With the appropriate conditions, the user is able to establish a streaming multi-media session with a low signal latency to provide good real-time interaction, and a low data error rate to provide good fault tolerance and error recovery. The user establishes the desired service during setup of the streaming multi-media session. The system then provides the requested service until the user terminates the session, or the user requests a change. However, if the streaming multi-media session is improperly terminated for any number of reasons, the user is unable to resume the streaming multi-media session at the exact point where they left off. As typically occurs in a streaming content session, the user must re-establish the session with the associated set-up and then replay the session up to the point of the termination or attempt to fast-forward to the point where the session was dropped or lost. If the streaming multi-media session is a live session, this may be impossible.
There are many reasons for the session to be improperly lost, dropped or terminated. One common reason for improper termination is movement of a mobile user from one cell to another cell in a cellular system. This is because cellular protocols do not adequately support streaming multi-media sessions that use address routed communications. Part of the problem is that there is little communication between the different communication layers. Changes in the transport or other lower layers can affect higher protocol or data layers. However, the techniques to exchange information between the layers are poor or non-existent.
In a streaming multi-media session, the data packets are most commonly transmitted over a packet switched network. This means that the packets and transmission system consistently rely on the source and destination addresses to properly route or switch the packets from the source to the destination. When a streaming multi-media session is established, the streaming server and the receiving or destination client exchange address information. This address information is then used during the streaming multi-media session as part of the address routing to send information packets between the server and the client. In a simplification, data packets from the server (the streaming source) include the client (destination) address in the data packet header. Data packets from the client (the stream receiver) include the server (streaming source) address in the data packet header. In this manner, the client and server are able to communicate with each other and maintain a duplex communication circuit. However, once the streaming multi-media session is established, the client and server do not expect the address information to change. Because the server does not expect the client address to change, when the address information does change in mid-session, the streaming multimedia session improperly terminates.
In a cellular system, as a mobile unit moves between cells, the supporting wireless communication circuits constantly set up and tear down the circuits between the base stations and the mobile unit. This occurs through a combination of information exchange between the mobile unit and the base stations over control channels, with set up and tear down of the communication channels for each cell. To the mobile voice communication user, the set up and tear down at the cell boundaries is usually transparent, or only a slight and momentary loss in signal quality. To the mobile data communication user, the set up and tear down may be noticed if the change occurs while a data packet is being transmitted. If the data packet is corrupted, the mobile unit will automatically request retransmission of the corrupted data packet. However, each such request also includes the mobile unit""s current address, so when the retransmission is requested after the mobile unit has completed the transfer to the new cell, the new mobile address will be included in the request and other than a short delay, the movement to a new cell will be transparent to the user.
However, in a UDP/IP streaming multi-media session to a mobile unit, with a TCP/IP control session, the packet address of the mobile unit, which is used for transmission of the multi-media data packets, is based on the IP address of the cell currently supporting the mobile unit. Accordingly, as the mobile unit moves from cell to cell, the data packet address of the mobile unit must also change. This means that as a mobile unit leaves one cell and enters another cell, any streaming multi-media session addressed to the mobile unit will improperly terminate because the IP address of the mobile unit changes. As described above, for non-continuous address routed data communication, such as web browsing, the mobile unit will have to reload the desired page if they are loading a page at the same time that they move from one cell to another cell. For a streaming multi-media session, the result of an IP address change is improper termination of the session and the need to set up the session all over again.
Systems and methods are needed to provide persistent communications in address routed communication systems, particularly streaming types of multi-media, in support of users with changing addresses.
In one aspect, the invention provides a method and apparatus for conducting an address routed communication session at a communication terminal. The terminal has a first address that is used to route session information from a session source to the terminal. The invention determines that the terminal requires a change of the first address to a second address during the communication session. The invention changes the terminal address from the first address to the second address without terminating the session, and continues the communication session using the second address to route session information from the session source to the terminal. The invention further captures transitory state information (such as frame number, sequence number and packet number) when the communication session is using the first address. The transitory state information is used to continue the communication session using the second address. The communication session may be one or more streaming multi-media sessions using internet protocol as the address routing scheme. The communication session may also be an internet telephony session. In one embodiment, the terminal is a cellular communication device using packet based addressing and the address change corresponds to a movement of the terminal from one cell to another cell. In this manner, a terminal is able to change address of a communication session without terminating the session.
In one aspect, the invention provides a method and apparatus for accomplishing the method with software or hardware contained within the mobile unit or terminal. In this manner, minimal changes are required to the underlying cellular and server architecture.
In one aspect, the invention provides a method and apparatus for accomplishing the method with a proxy server and software or hardware contained within the proxy server. In this manner, minimal changes are required in either the mobile unit operation and software, or the session server architecture.
The foregoing specific aspects and advantages of the invention are illustrative of those which can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages that can be realized. Thus, the objects and advantages of this invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variations which may be apparent to those skilled in the art. Accordingly the present invention resides in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.